The objective of my proposed research is to investigate the hypothalamic control of prolactin secretion by the anterior pituitary gland of the rat. Evidence is accumulating that dopamine is a physiological prolactin inhibiting factor (PIF) and that thyrotropin releasing factor (TRF) is a physiological prolactin releasing factor (PRF). We will collect hypophysial stalk blood for measurement of dopamine by a liquid chromatographic-electrochemical method we have developed and for measurement of TRF by radioimmunoassay. To determine if physiological stimuli (suckling, mating, and estrogens) alter prolactin secretion by altering release of dopamine or TRF, we will measure the levels of these hypophysiotropic hormones after application of the physiological stimuli. This will be done in animal model systems previously established to respond to prolactin releasing stimuli even in the anesthetized state: 1) to simulate suckling, the isolated mammary nerve will be electrically stimulated in urethane-anesthetized rats; 2) to simulate mating, the isolated pelvic nerve will be electrically stimulated in urethane-anesthetized rats; 3) the Althesin-anesthetized estrogen-treated rat will simulate the proestrus prolactin surge. We will also continue to work on the development of an electrochemical probe for implantation into the median eminence for direct in situ recording of the changes in dopamine concentration occurring after application of physiological stimuli. The effect of neurotransmitters (serotonin, acetylcholine and histamine) and of neuropeptides (substance P, neurotensin and beta-endorphin) - all of which are found in high concentration in the median eminence and all of which affect prolactin secretion via hypothalamic action - on dopamine and TRF release into stalk blood will also be investigated. These studies will allow us to specify more completely the hypothalamic mode by which physiologic stimuli release prolactin. Moreover, the results may help to explain the galactorrhea-amenorrhea syndrome in women which is being observed more and more frequently.